Cell cycle checkpoint

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Cell cycle checkpoints exist at specific points in the cell cycle in eukaryotic cells to prevent them from progressing to the next phase of the cell cycle in the event of DNA damage or another condition which would make cell division dangerous for the cell. Feedback from the cell about its size and condition of its chromosomes determines whether the cell cycle does or does not progress; the feedback can either trigger subsequent phases or delay them to allow time for the current phase to be completed. Within the cell there are many Cyclin Dependent Kinase (CDK) molecules that are used in the signalling and decision of the checkpoints.

There are 3 main checkpoints which control the cell cycle in eukaryotes.

Contents 1 G1 Checkpoint 2 G2 Checkpoint 3 Anaphase Checkpoint 4 References

[edit] G1 Checkpoint

The first checkpoint is located at the end of the cell cycle's G₁ phase, just before entry into S phase, making the key decision of whether the cell should divide, delay division, or enter a resting stage. Most cells stop at this stage and enter a resting state called G₀. Liver cells for instance only enter mitosis around once or twice a year. The G₁ checkpoint is where eukaryotes typically arrest the cell cycle if environmental conditions make cell division impossible or if the cell passes into G₀ for an extended period. In animal cells, the G₁ phase checkpoint is called the restriction point, and in yeast cells it is called the start point.

[edit] G2 Checkpoint

The second checkpoint is located at the end of G₂ phase, triggering the start of the M phase (mitosis). In order for this checkpoint to be passed the cell has to check a number of factors to insure the cell is ready for mitosis. If this checkpoint is passed, the cell initiates the many molecular processes that signal the beginning of mitosis. The CDK's associated with this checkpoint are activated by the removal of an inactivating phosphate by the action of a "Maturation promoting factor" (MPF). The MPF activates the CDK in response to environmental conditions being right for the cell and allows the cell to begin DNA replication.

[edit] Anaphase Checkpoint

The third checkpoint occurs during anaphase, triggering both the exit from mitosis and the beginning of cytokinesis. The Cdh1 binds to the anaphase promoting complex, starting the destruction of the mitotic cyclins.^[1] After the cell has split into its two daughter cells the cell enters G₁.

[edit] References

1. ^ Karp, Gerald (2005). Cell and Molecular Biology: Concepts and Experiments, 4th Edition. Hoboken, NJ: John Wiley and Sons, 598-599. ISBN 0471162310.